508 



Subsurface Geologic Methods 



As the bit is too small to pass through the ring, it lifts the whipstock off 

 bottom, withdrawing it from the hole. If an increase in deflection is de- 

 sired, additional footage of "rathole" is made with a follow-up bit, after 

 which all of the "rathole" is reamed to full gauge with a pilot reamer. 

 In case the deflection of the small hole made in drilling off the whipstock 

 is considered sufficient, the follow-up run is omitted. The hole must be 

 opened to full gauge in either case. Rock bits are used for drilling off 

 a whipstock in hard formations. 



A recent development in the use of a removable whipstock in ex- 

 tremely hard rock has been the adaptation of a diamond-type whipstock 

 bit. A number of successful sidetracking operations using this bit have 



Figure 239. Operation of whipstock. Left to right, (1) on bottom in oriented position; 

 (2) pilot hole made; (3) picking up whipstock; (4) reaming pilot hole to full 

 gauge. 



